Bite Performance of Captive Alligator Snapping Turtles (Macrochelys temminckii) Improves after Reintroduction
Alligator Snapping Turtles (Macrochelys temminckii) possess unique head morphology that suggests strong natural selection for bite performance, which likely influences foraging and prey selection, as well as the outcomes of intrasexual aggressive encounters, mating, and defense against predators. Therefore, bite performance has the potential to directly and indirectly impact fitness. In this study, we assessed the effects of captivity on bite force by comparing the performance of captive and reintroduced M. temminckii. On average, free-ranging M. temminckii bite with greater force than do individuals residing in captivity, and captive individuals housed under seminatural conditions in outdoor ponds outperformed those housed indoors. Further, we found that free-ranging M. temminckii released into different river systems performed comparably and required less provocation than captives to display gaping and biting behavior. It remains to be determined whether the observed performance differences were more strongly influenced by physiological limitations on muscle performance or by behavioral variation in motivation to bite with maximum force.ABSTRACT
Anatomical locations of head dimension measurements of Macrochelys temminckii, including head length (yellow), head width (teal), and head height (purple).
A juvenile Macrochelys temminckii demonstrating a defensive posture that includes shell-raising and displaying a defensive gape.
Maximum bite force of (A) captive-reared Macrochelys temminckii housed indoors and outdoors, (B) head-started, free-ranging Macrochelys temminckii inhabiting the Caney and Verdigris Rivers in northern Oklahoma, and (C) lumped captive and lumped free-ranging Macrochelys temminckii from all locations. Note that all axes are log10-transformed. Regression statistics are as follows: outdoor captive (y = 0.81x – 0.64, r2 = 0.95, P < 0.0001), indoor captive (y = 0.69x – 0.37, r2 = 0.88, P < 0.0001), Verdigris River (y = 0.66x – 0.03, r2 = 0.40, P < 0.001), Caney River (y = 0.80x – 0.51, r2 = 0.81, P < 0.0001), lumped captive (y = 0.76x – 0.53, r2 = 0.91, P < 0.0001), and lumped free-ranging (y = 0.81x – 0.55, r2 = 0.75, P < 0.0001).
Frequency of Macrochelys temminckii bites by group that required no provocation to elicit a gape or bite, and frequencies of pre-bite aggression displays by group including lunging, shell-raising, or snapping. Pre-bite aggression is denoted by black, immediate gape by light gray, and immediate bite by dark gray.
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